Cellulose is the most abundant organic renewable polymer available. Its structure consists of linear chains of (β)-1,4-linked anhydro-D-glucose units. Each of these units has three hydroxy groups available for functionalization. For wood pulp, the degree of polymerization (DP) can lie between 300 and 1700, with every unit corkscrewed 180° with respect to its neighbors:
This structure provides cellulose polymer chain with extensive hydrogen-bonding possibilities as well as high chain stiffness.
In recent years, cellulose derivatives as well as other biopolymers have been studied as potentially efficient, cheap, renewable and biodegradable supports for catalysis, that is, heterogeneous catalysis, wherein the catalyst is normally solid (bulk catalyst) or can be supported on a solid support (supported catalysts) and the reactants are fluids (liquids or gases). For instance, hybrids made of bulk cellulose supporting Pd(0) and Cu(0) nanoparticles (NPs) proved active for the catalysis of C—C coupling reactions and of the N-arylation of nitrogen heterocycles respectively in organic solvents. Pd(II) complexes could also be stabilized onto cellulose and catalyze the Heck reaction in water. For homogeneous catalysis, the catalyst is in the same phase as the reactants, for example, all reactants and the catalyst are solubilized, dispersed or suspended in water. In other approaches, bulk cellulose was used as a precursor of microporous carbon supports for catalytic hybrids.